This seminar, sponsored by the National Institute for Environmental Health Sciences (NIEHS) and U.S. EPA Office of Emergency and Remedial Response, is the last in a series of three seminars examining current research on PCBs sponsored by EPA and the National Institute of Environmental Health Sciences (NIEHS). Because of their once-popular commercial uses, improper disposal and environmental persistence, polychlorinated biphenyls (PCBs) are common environmental contaminants found in many designated Superfund sites. This event will highlight the cutting edge research being conducted by NIEHS scientists into the non-cancer endpoints of exposure to PCBs. Recognition of polychlorinated biphenyls (PCBs) and related compounds as potential human neurodevelopmental toxicants was largely a consequence of two mass poisonings in Japan (1968) and Taiwan (1979). Dr. Susan Korrick, of Harvard University, will review findings from the population-based epidemiologic studies for which prenatal PCB exposure measures are available. The particular emphasis will be on findings related to growth and neurocognitive development in infancy and later childhood. Additionally, Dr. Rita Loch Caruso, of the University of Michigan, will discuss her findings that acute in vitro exposures to commercial PCB mixtures and microbially dechlorinated commercial PCB mixtures increase the frequency of spontaneous contractions of uteri from pregnant rats. Increased uterine stimulation was observed with PCB mixtures containing increased abundance of lesser-chlorinated, ortho-substituted congeners. By showing that PCBs stimulate uterine contraction in vitro, these studies provide a biologically plausible mechanism by which PCB exposures could decrease gestation length.